The present invention relates to a device for generating an electric voltage.
A known rotational rate sensor produced by microsystem technology has an oscillating weight which oscillates about its axis of rotation. The oscillating weight has a comb structure, i.e., it is formed by a comb structure which alternately meshes with a first stationary comb structure and with a second stationary comb structure of the sensor as it oscillates. This arrangement forms two capacitors whose capacitances change in opposite directions over time. If the rotational rate sensor experiences a rotational rate perpendicular to the axis of torsional vibration of the oscillating weight, one side of the oscillating weight moves toward the substrate of the rotational rate sensor and the other side moves away from it. These changes in distance are measured capacitively by electrically conducting surfaces beneath the oscillating weight. The comb structures which are stationary with respect to the sensor and the comb structure which is provided on the oscillating weight are acted upon by an alternating voltage, thereby inducing oscillation of the oscillating weight.
To obtain a high signal-to-noise ratio of the test signal which represents the rotational rate, the deflection of the moving structure of the sensor must be maximized.
In the case of a known capacitive micromechanical sensor, such as a rotational rate sensor manufactured by planar silicon processes in particular, the change in capacitance depends not only on the deflection of the moving structure but also on the gap distance. Gap distance is understood to refer to the average distance between the xe2x80x9cteethxe2x80x9d of the movable comb structure and the two stationary comb structures in the case of a stationary oscillating weight. Since the gap distance may vary from one sensor to the next due to the manufacturing technology, each sensor must be adjusted individually to achieve maximum deflection, i.e, maximum vibration amplitude of the movable structure. Not only is this complicated, but it may also result in the movable structure striking against the stationary structure, which could damage the sensor.
The device according to the present invention has the advantage over the related art in particular that, regardless of the manufacturing tolerances, it automatically adjusts a predefined deflection of the oscillating weight of a capacitive or inductive sensor. This eliminates individual manual adjustment of each sensor for setting a virtually maximum deflection of the oscillating weight in order to obtain a maximum signal-to-noise ratio. This makes it possible to manufacture capacitive and inductive sensors such as rotational rate sensors in particular less expensively.